1. Field of the Invention
The present invention relates to the field of high-pressure fluid pumps, and in particular, diagnosing malfunctions in high-pressure fluid pumps.
2. Description of the Related Art
High-pressure fluid pumps are used in various industrial applications. For example, a high-pressure pump may be used to provide a pressurized stream of water for cleaning and surface preparation of a wide variety of objects, from machine parts to ship hulls.
High-pressure pumps may also be used to provide a stream of pressurized water for water jet cutting. In such an application, a pump pressurizes a stream of water, which flows through an orifice to form a high-pressure fluid jet. If desired, the fluid stream may be mixed with abrasive particles to form an abrasive waterjet, which is then forced through a nozzle against a surface of material to be cut. Such cutting systems are commonly used to cut a wide variety of materials, including glass, ceramic, stone, and various metals, such as brass, aluminum, and stainless steel, to name a few. A single pump may be used to provide pressurized fluid to one or several tools.
Pumps of this type may develop fluid pressures exceeding 60,000 psi. FIG. 1 illustrates an example of such a pump. FIG. 1 shows a pump 100 having three cylinders 102. Each of the three cylinders 102 is coupled to a crankshaft 104 by a connecting rod 106. The connecting rods 106 are distributed on the crankshaft 104 in a known way, such that the plunger 108 of each of the cylinders cycles through a compression and intake cycle 120° ahead of one of the remaining plungers, and 120° behind the other remaining plunger. The pump 100 is coupled to a drive source (not shown) via a driveline 110. The drive source may be an electric motor, a diesel powered engine, or any other drive means capable of generating sufficient force.
As will be recognized, the operation of each one of the cylinders is substantially identical to that of the other two, albeit out of phase therewith. A detailed description of the operation of one such pump may be found in U.S. Pat. No. 6,092,370, issued on Jul. 25, 2000, in the name of Tremoulet, Jr. et al., which patent is incorporated herein in its entirety.
With reference now to FIG. 2, as described in the aforementioned patent, each cylinder 102 of the pump 100 includes an intake check valve 112, which permits fluid to enter the chamber 128 via an inlet port 114 during an intake stroke of the plunger 108; each cylinder 102 includes a primary seal 116 and static seals 118, which prevent fluid from escaping the chamber 128 during a pressurizing stroke of the plunger 108; and finally, each cylinder includes an outlet check valve 120, which vents pressurized fluid into an outlet chamber 122. From the outlet chamber 122, the pressurized fluid flows through an outlet port 124 to a high-pressure manifold 126, where fluid from each of the three cylinders 102 is collected, to be distributed to a tool or tools according to the requirements of the particular application.
A particular problem with such pump systems is detecting, and diagnosing, malfunctions of components of individual cylinders. As previously explained, such pumps may operate in pressure ranges up to, and exceeding, 70,000 psi. In a condition where a load on a pump is less than the pump's maximum capacity, a failure of, for example, a static seal in one of a plurality of cylinders is not sufficient to show up as a drop in overall pressure at the high-pressure manifold, or at the tool or device being driven by fluid pressure. Nevertheless, such a failure reduces the overall capacity of the pump, such that, when an increased load is placed on the pump, it is not capable of providing its rated maximum output. Other types of malfunctions may do more than reduce the overall capacity of the pump, but may cause significant damage to the pump. For example, a failure of the outlet check valve 120 of one cylinder, such that the valve remains open during both the intake stroke and the pressurizing stroke of the plunger, will create a situation in which pressure from the high-pressure manifold drives fluid back into the cylinder during the intake stroke. Consequently, pressure within the cylinder remains at, or near, the rated output pressure of the pump. With such constant pressure on the plunger, components linking the plunger to the crankshaft are not effectively lubricated, resulting in friction, and eventual seizing of the pump. Thus, undetected breakdown of an inexpensive component may lead to catastrophic failure of the pump.
A known method of detecting such failures is through the placement of temperature sensors at various points on each of the cylinders. It is known that, in the case of many types of malfunctions, the malfunctioning device will generate heat in the valve casing immediately around that component. Thus, by monitoring temperature levels at various points on the pump body, malfunctions may be detected and diagnosed. The '370 patent, previously mentioned, describes such a method.
While the use of temperature sensors is superior to other known methods of fault detection, it does have some drawbacks. For example, heat build up, due to a malfunction, does not occur instantaneously. Thus, a problem cannot always be detected before serious damage to the pump occurs. Another problem is the complexity and cost of such a monitoring system. An effective monitoring system may include three or more sensors per cylinder. So, a pump having three cylinders will require up to nine sensors, together with the necessary signal conditioning circuitry and diagnostic circuitry for effective monitoring. During service the sensors must be removed, then reinstalled after servicing. Additionally, such systems must be calibrated with the particular pump and are prone to damage, as they are not robust in nature.